The present invention relates generally to the production of bent sheets or plates of glass and, more particularly, to an improved method and apparatus for bending glass sheets to relatively sharp angles.
One well-known technique for bending glass sheets, such as those intended for use as glazing closures in vehicles or the like, utilizes a ring or skeleton-type bending mold having shaping surfaces adapted to engage only the marginal edge portions of the sheets, to avoid marring the viewing area of the finished glazing closure, and conforming in elevation to the curvature of the sheet when bent. According to this technique, a flat sheet of glass is supported on the mold above the shaping surface and is heated in a furnace to a temperature corresponding to the softening point of glass whereupon the sheet sags by gravity into engagement with the shaping surfaces of the mold. Very often, the mold is sectionalized to permit relative movement of the sections thereof during the sagging of the heated glass to impart rather complex curvatures to the glazing closures incorporated in modern day vehicle designs, for example. While the bent sheet is still resting on the mold after being shaped to the desired configuration, it is cooled or annealed in a controlled manner to a point below the annealing range of glass.
In addition to the complex curvatures mentioned above, it is often desirable to provide a relatively sharp angled or V-shaped bend in the glazing closure transversely or longitudinally thereof along one or more lines to effect wrap-around of a windshield or backlight into the roof line of the vehicle or into the side surfaces thereof. The formation of such bends, i.e., V-shaped bends or bends having very small radii of curvatures, by the above described "gravity" bending technique poses problems in fabrication.
A solution to such problems was provided by the glass bending methods disclosed and claimed in U.S. Pat. Nos. 3,762,903 and 3,762,904, assigned to the same assignee as the present invention, whereby an electrically conducting path is formed on at least one surface of the glass sheet along the line about which it is desired to sharply bend the sheet. The sheet is then supported on a suitable mold structure and heated in a furnace to a temperature corresponding to the softening point of the glass, causing it to sag by gravity into conformance with the shaping surfaces of the mold while simultaneously passing an electric current through said path to heat the area of the glass sheet immediately adjacent said path to a temperature above the aforementioned softening point, causing said sheet to bend along said path to form the desired relatively sharp angle therein. It can be appreciated that in a completely automated, mass production operation, means must be provided for supplying current to the electrically conducting path automatically during the transport of the glass through the heating furnace.